Inhibitory activity of Australian culinary herb extracts against the bacterial triggers of selected autoimmune diseases

Abstract

Introduction: High antioxidant capacities have been linked to the treatment of rheumatic diseases and in the inhibition of microbial growth. Recent reports have identified several native Australian culinary herbs with high antioxidant capacities. Despite this, several of these species are yet to be tested for the ability to inhibit the growth of the bacterial triggers of autoimmune inflammatory diseases. Methods: Solvent extracts prepared from selected Australian culinary herbs were analysed for antioxidant capacity by the DPPH free radical scavenging assay. Growth inhibitory activities against bacterial species associated with initiating rheumatoid arthritis and ankylosing spondylitis were determined by disc diffusion assay and quantified by MIC determination. Toxicity was determined by Artemia franciscana bioassay. Results: Methanolic extracts of most plant species displayed relatively high antioxidant contents (equivalent to approximately >10 mg of vitamin C per gram of fruit extracted). Most aqueous extracts also contained relatively high antioxidant capacities. The ethyl acetate and chloroform extracts generally had lower antioxidant capacities than the more polar extracts. In contrast, the hexane extracts of all species had low antioxidant contents (generally < 0.5 mg of vitamin C per gram of fruit extracted). Interestingly, the bacterial growth inhibitory activity of the extracts did not correlate with their antioxidant capacities. With the exception of native thyme, the herb extracts with the highest antioxidant capacities had only low antibacterial activity, with MIC values generally well in excess of 4000 µg/ml against all bacterial species. In contrast, many of the ethyl acetate extract and hexane extracts, which had low range antioxidant capacities (generally < 5 mg ascorbic acid equivalents/g extracted), had potent bacterial growth inhibitory activity with many MIC values substantially below 1000 µg/ml). The river mint ethyl acetate extract displayed toxicity in the Artemia franciscana bioassay (LC50=186 µg/mL). All other extracts were nontoxic. Conclusion: The lack of toxicity and inhibitory activity against microbial triggers of rheumatoid arthritis and ankylosing spondylitis by the Australian native culinary herb extracts indicates their potential in the treatment and prevention of these diseases.

Acai, cacao and maca extracts: Anticancer activity and growth inhibition of microbial triggers of selected autoimmune inflammatory diseases

“…Extracts from other high antioxidant fruits are good inhibitors of cancer cell growth and their anti-proliferative efficacy is often related to the antioxidant capacities of the extracts. 18,49 In contrast to these previous reports, the anti-proliferative activities of the acai, cacao and maca extracts observed in our study did not correlate with their measured antioxidant capacities. Indeed, the most potent inhibitor of CaCo2 proliferation was the aqueous maca extract (IC 50 1800 µg/mL).…”

“…Many high antioxidant fruits and herbs have been reported to have good antibacterial activities. [12][13][14][15][16][17][18][19]21,33,36 Given the high antioxidant capacities and 'superfood' status of acai, cacao and maca, surprisingly few studies have examined their ability to inhibit the growth of pathogenic bacteria. Indeed, whilst multiple anecdotal reports are available, we were unable to find any scientific studies screening acai, cacao or maca extracts for the ability to inhibit the growth of P. mirabilis, K. pneumoniae, A. baylyi or P. aeruginosa.…”

“…[12][13][14] Furthermore, potent growth inhibition has been reported for several high antioxidant fruits [15][16][17] and culinary herbs. 18 Particularly noteworthy, Terminalia ferdinandiana (Kakadu plum), Tasmannia lanceolata (mountain pepperberry) and several Syzygium spp. (which are often referred to as 'superfoods' due to their extremely high antioxidant capacities) are potent growth inhibitors of microbial triggers of rheumatoid arthritis (Proteus mirabilis), 19 ankylosing spondylitis (Klebsiella pneumoniae) 20 and multiple sclerosis (Acinetobacter baylyi and Pseudomonas aeruginosa).…”

Growth inhibition of the zoonotic bacteria Bacillus anthracis by high antioxidant Australian plants: New leads for the prevention and treatment of anthrax

“…The Illawarra plum, lemon aspen, desert lime, wattle seed, native thyme and rivermint were particularly potent inhibitors of the microbial triggers of rheumatoid arthritis and ankylosing spondylitis. 24,25 All of the bacterial species associated with the onset of the autoimmune diseases screened in the previous studies are Gram negative and thus substantially different to the Gram positive B. anthracis screened in this study. However, the previously reported inhibitory activity does indicate the presence of antibacterial components in these extracts and is consistent with the inhibitory activity reported in this study.…”

“…Recently, we also reported growth inhibitory activity of several high antioxidant fruits [22][23][24] and culinary herb extracts 25 against some microbial triggers of selected autoimmune inflammatory diseases. The Illawarra plum, lemon aspen, desert lime, wattle seed, native thyme and rivermint were particularly potent inhibitors of the microbial triggers of rheumatoid arthritis and ankylosing spondylitis.…”